The present invention relates to information handling systems and, more particularly, it is concerned with an apparatus that is capable of both digitizing and plotting graphic information on sheet material.
U.S. patent application Ser. No. 377,769, filed July 9, 1973 and entitled "Interactive Graphic System" discloses an information processing system including a plotting table having a manually operable cursor for digitizing graphic information defined on sheet material spread on the table. Digitizing, as used in this application, refers to the reduction to point-data of continuous or intermittent graphic characters such as lines and intersections. Such reduction of graphic information to point data represented by electrical or other signals is necessary for handling and processing the information in computers or transmission equipment in a recognizable and easily utilized form.
The apparatus shown in the above-identified application is also capable of plotting graphic information from electrical or other signals produced by a computer or a memory device in which plotting programs are held in either temporary or permanent storage. Plotting may be considered to be the converse of digitizing to the extent that point data is converted from an electrical or other signal to a graphic form.
The cursor shown in the above-identified application is mechanically suspended from the carriage that carries the plotting pen which thereby limits the ease with which the cursor can be moved to different coordinate locations on sheet material bearing graphic information. To a lesser degree, the mechanically attached cursor also reduces the ability of the plotting instrument to be moved or accelerated over a plotting surface because of the inertia added to the carriage by the cursor.
A system having a free cursor is more responsive in that carriage movements are faster parallel to the sheet material receiving or bearing graphic information. Prior art apparatus having a free cursor for digitizing alone is shown in U.S. Pat. No. 3,636,256 entitled "Chart-Reading Apparatus". The cursor is manually moved over a supporting surface on which sheet material bearing graphic information is positioned and an electromagnetic coil on the cursor is connected to synchronous detection circuitry for determining the location of the cursor on the supporting surface. A movable carriage is mounted below the supporting surface and carries electromagnetic field coils which induce currents in the coil on the cursor. By selectively exciting the electromagnetic field coils on the carriage, it is possible to determine the relative positioning of the carriage and cursor and to slave the carriage to follow the cursor movements on the supporting device. Positioning the cursor on selected locations and recording the carriage positions which correspond with the cursor positions digitizes the selected locations.
Although the carriage below the supporting surface provides a surface which is completely exposed and unobstructed, the utility of the apparatus is limited to the digitizing function. Since the principal components of a plotting instrument are provided by the supporting surface, the carriage which is movable in two coordinate directions parallel to the supporting surface and the servo-drive mechanism which controls the movements of the carriage, it would be advantageous if the apparatus could be redesigned to perform both digitizing and plotting operations.
It is accordingly a general object of the present invention to disclose a servocontrolled mechanism which is capable of use as a digitizer or a plotter.